ESR1 and breast cancer: Breast cancer has been identified as having at least four subtypes: luminal-like, HER2-positive, basal-like, and normal-like.11,12 In clinical practice, IHC results on ER, PgR, HER2, and Ki67 status can be used to approximately classify breast cancer into the above subtypes.13 CNB is widely used in BC diagnosis and ER, PR, HER2, and Ki67 status evaluation.